In a computer system handling important data, a so-called redundant configuration is adopted, where many components are duplicated to prevent system failure or data loss caused by the failure of a component. The components within the storage subsystem and the paths (access paths) connecting the host computer and volumes of the storage subsystem are not an exception. In many cases, a configuration is adopted where the controller of the storage subsystem is duplicated, and the access paths connecting the host computer and the volumes of the storage subsystem are also duplicated. Thereby, continuous operation is made possible even when failure occurs to the controller, or when failure such as disconnection occurs to the access path.
Generally, in a storage subsystem where the controller is duplicated, when the host computer issues access requests to either one of the controllers, the access performance is not the same in many cases. For example, in a storage subsystem where two controllers, controller A and controller B, are installed, the access performance realized when an access request to a certain volume is issued to controller A may be lower than the access performance realized when the access request is issued to controller B. In other words, the performance may vary depending on the selection of the access path by the host computer.
A function to notify the priority of access paths from the storage subsystem to the host (ALUA (Asymmetric Logical Unit Access)) is known (Patent Literature 1). According to Patent Literature 1, a host having received information related to a priority of an access path from a storage subsystem executes access to the storage subsystem using a prioritized path, and when the prioritized path cannot be used due to failure, the host executes access to the storage subsystem using a non-prioritized path.